The Waukesha County Sheriff's Department's arson team is working with the Bureau of Alcohol, Tobacco, Firearms and Explosives to determine the cause of the fire that destroyed nearly three dozen buses in a bus yard Sunday.

"And then all of a sudden, I started to hear the explosions," said Bill Hupe, who lives nearby. "You could feel the concussion, but I think mainly it was the tires blowing and probably some gas tanks."

Fire departments from the town of Lisbon, village of Hartland, village of Sussex, Stone Bank, Lake Country, Pewaukee, city of Waukesha, town of Delafield, Okauchee, village of Hartland, city of New Berlin, Wales Genesee, village of Menomonee Falls, Richfield, village of Dousman, city of Brookfield, town of Brookfield, village of Butler, town of Waukesha, Ashippun, city of Oconomowoc, village of North Prairie, Tess Corners and Mukwonago responded to assist.

Officers from the village of Chenequa Police Department and town of Oconomowoc Police Department responded to assist as well, Sheriff Eric Severson said.

Buses ran on time Monday for all of the Arrowhead area schools the company serves.

"The outpouring of support from numerous other bus companies around the state and local businesses and individuals is truly humbling. We can’t thank them enough as we work to get our operations back to normal," Dousman Transport Co. President Robert Nelson told WISN 12 News.

An environmental cleanup team is now scraping top soil from ditches surrounding the bus yard after diesel fuel leaked from the tanks of flaming school buses.